In recent years, a radiological image detection apparatus using an FPD (Flat Panel Detector) for detecting a radiological image to generate digital image data has been put to practical use, and is being widely used rapidly due to a merit that an image may be confirmed in real time as compared with a conventional imaging plate. There are various types of such radiological image detection apparatuses. As one example, an indirect conversion type has been known.
The indirect conversion type of radiological image detection apparatus includes a scintillator formed by a fluorescent material which emits fluorescence by radiation exposure, such as CsI or NaI, and a sensor panel which has two-dimensionally arrayed photoelectric conversion elements. Radiation transmitted through a subject is firstly converted into light by the scintillator, and the fluorescence of the scintillator is photoelectrically converted by a group of photoelectric conversion elements of the sensor panel, thereby generating an electrical signal (digital image data).
In the radiological image detection apparatus, there is also known a technology for forming a scintillator by a group of columnar crystals of a fluorescent material such as CsI for the purpose of improving the sensitivity (e.g., see Patent Literature 2). The columnar crystals are typically formed by growing crystals of the fluorescent material into columnar shapes on a support by a vapor deposition method. As the support, a sensor panel or a suitable substrate is used. When the sensor panel is used as the support, a group of columnar crystals are directly formed on the sensor panel. Also, when a suitable substrate is used as the support, a group of columnar crystals formed on the substrate are bonded to the sensor panel. The columnar crystals formed by the vapor deposition method do not include impurities such as a binder, and also have a light guide effect which guides fluorescence generated in the columnar crystals in the crystal growth direction, thereby suppressing the fluorescence from being diffused. This improves the sensitivity of the radiological image detection apparatus, and also improves the sharpness of an image.
The columnar crystals are grown almost perpendicularly to the surface of the support. Thus, in the case of bonding the group of the columnar crystals formed on the substrate to the sensor panel as well as in the case of using the sensor panel as the support, the respective columnar crystals are provided almost perpendicularly to the surface of the sensor panel. When the sensor panel is flat, radiation has a large incident angle with respect to the columnar crystals provided perpendicularly to the surface of the sensor panel so that it may be deviated from the center of the irradiation field. Thus, the radiation proceeds through a plurality of columnar crystals, thereby lowering the sharpness of an image.
Therefore, in the radiological image detection apparatus disclosed in Patent Literature 2, a flexible sensor panel is used, in which the sensor panel is curved so that respective columnar crystals may be parallel to radiation which is radially widened. In each portion of the irradiation field, the respective columnar crystals become parallel to the radiation, thereby suppressing sharpness of an image from being lowered.